The adjustment screws are under those black caps in the picture. They may be slotted, splined, half round or some other shape. To adjust them, first find out their shape, then you may be able to find the proper tool. O'Rieleys has a tune kit that may work. You can thank the epa for the weird shapes, they think that they can bring about cleaner air by making it difficult to adjust the carbs andhave mandated the strange shapes to the manufacturers.